This study was performed to determine the feasibility of second hematopoietic stem cell transplantation (HSCT) using reduced-intensity conditioning (RIC) with fludarabine and melphalan in patients with relapsed hematologic malignancies after a prior autologous HSCT. Twelve patients (multiple myeloma [n = 7], non-Hodgkin lymphoma [n = 3], and acute myeloid leukemia [n = 2] received allogeneic HSCT using RIC with fludarabine (25 mg/m(2) for 5 days) and melphalan (140 mg/m(2) for 1 day) after a failed autologous HSCT. The graft-versus-host disease (GVHD) prophylaxis consisted of cyclosporine plus a minidose of methotrexate. All patients achieved a neutrophil and platelet engraftment in a median 13.5 days and 17.5 days, respectively. The transplant-related mortality was 2 patients (16.7%). Grade II-IV acute GVHD and chronic extensive GVHD were noted in 4 (33.3%) and 1 patient (11.1%), respectively. Over a median follow-up duration of 376 days, 5 patients were alive without evidence of disease. The estimated nonrelapse mortality at 1 year was 28.4%. The estimated overall survival rate at 1 year was 58.3%, and the estimated event-free survival rate at 1 year was 41.7%. Allogeneic HSCT using RIC with fludarabine and melphalan appears to be feasible for a second HSCT in patients with relapsed hematologic malignancies after a failed autologous HSCT